Just because you need another reason to exercise.

A recent study by a group at the UAB Department of Nutrition Science claims that body composition may have an impact on the growth and spread of cancer. Traditional views have pointed towards calorie intake as the main problem in obesity, but it seems that what the body does with these calories is the main concern.

In the first experiment, mice genetically prone to pancreatic cancer were kept at two temperatures -- the cooler the ambient temperature, more energy (as calories) is required to maintain normal body functioning -- and fed the same amount of food. The mice kept closest to normal body temperature predictably became more obese than the other set, but also became significantly more inundated with cancer. The mice that had to expend more energy in the cooler environment retained generally normal pancreas tissue.

To further clarify this result, the researchers kept the mice at different temperatures, but allowed them full access to as much food as they could take in. This would keep both sets of mice at a relatively similar body composition to show whether actual food intake or the controlled temperature had any effect on the spread of cancer. In this scenario, the mice held at the lower temperature consistently ate more, had similar body mass, and thus had similar instances of cancer as the other group.

The actual link between obesity and cancer is still unclear. Leptin seems a likely candidate, as this hormone is not only involved with fat retention, but also in the induction of oxidative stress (cell damage caused by the creation of oxygen free radicals also linked to aging, neurodegenerative disease, and cancer). As a hormone, increased leptin is supposed to tell the brain when hunger is satisfied and to stop eating. But people suffering from obesity are resistant to its effects (much as they are similarly resistant to effects of insulin, thus the increase in occurence of type II diabetes). More and more leptin is produced without satiating effect, wreaking havok on other systems. The transgenic obese (ob/ob) mouse shown in the picture above has a mutation in which its brain is similarly resistant to leptin. The cancerous mice in the study were shown to have a huge increase in internal leptin levels.

So what does all of this mean? Well, basically, leaner bodies tend to handle calories better. Of course, this doesn't increase drug companies' revenues or really help anyone's day-to-day lives. Even though the research shows that caloric intake doesn't in itself cause cancer, excessive eating does lead to increased body fat, obesity, and then disease. Though maybe lowering the thermostat a few degrees over these winter months couldn't hurt.